Double-tracer autoradiographic study of protein synthesis and glucose consumption in rats with focal cerebral ischemia.

A double-tracer autoradiographic method for simultaneous measurement of regional glucose utilization (rCMRglc) and regional protein synthesis (PS) in consecutive brain sections is described and applied to study the metabolism of the ischemic penumbra 2 h after occlusion of the middle cerebral artery (MCAO) in rats. In halothane anesthesia, the left middle cerebral artery was permanently occluded. Two hours after MCAO an i.v. bolus injection of 14C-deoxyglucose and 3H-leucine was given and circulated for 45 min. Two sets of brain sections were processed for quantitative autoradiography. Neighboring brain sections exposed an X-ray film (3H-insensitive), and a 3H-sensitive for determination of rCMRglc and PS, respectively. Sections for PS determination were washed in trichloroacetic acid (TCA) prior to film exposure in order to remove 14C-deoxyglucose and unincorporated 3H-leucine. Regional rates of PS and glucose utilization were measured by densitometric image analysis. Normal rates of metabolism were defined as mean +/- 2 SD of values in the non-ischemic cortex. The volumes of ischemic cortex displaying normal rates of PS and glucose utilization, respectively, were measured. The cortical volume with normal PS was significantly less than that of normal rCMRglc: 142 (127-147) mm3 vs. 203 (184-206) mm3. Treatment with the glutamate antagonists MK-801 (1 mg kg-1) and NBQX (30 mg kg-1 x 2) did not significantly change this, although MK-801 tended to reduce the size of the metabolic penumbra calculated as the difference between ischemic cortex with reduced PS and ischemic cortex with reduced rCMRglc.     

Human brain glucose utilization and cognitive function in relation to age

Brain oxidative metabolism was examined with positron emission tomography and {¹⁸F}2-deoxy-D-glucose in 40 healthy men aged 21 to 83 years, under conditions of reduced visual and auditory stimulation. The mean cerebral metabolic rate for glucose (CMR_glc) equaled 4.6 to 4.7 mg. 100 gm^?1· min^?1 and did not correlate significantly with age (p > 0.05). Regional cerebral metabolic rates for glucose (rCMR_glc) and Q ratios (rCMR_glc/CMR_glc), which had lower coefficients of variation than did rCMR_glc, also did not correlate with age. Hyperfrontality of cerebral metabolism was absent at all ages. Age decrements were demonstrated in the error score on the Benton Revised Visual Retention Test and in the Performance Subtest scaled score of the Wechsler Adult Intelligence Scale (WAIS) but not in the Verbal Subtest scaled score of the WAIS. The cognitive test scores did not correlate with brain metabolic rates. The results indicate that brain oxidative metabolism, when measured under resting conditions with reduced sensory input, is not reduced in relation to age in healthy men. Furthermore, no significant relations between intelligence and resting cerebral metabolism are evident.     

In vivo imaging of brain incorporation of fatty acids and of 2-deoxy-d-glucose demonstrates functional and structural neuroplastic effects of chronic unilateral visual deprivation in rats

Regional cerebral ‘incorporation coefficients’k^* of each of 3 labeled long-chain fatty acids — [9,10-³H]palmitate ([³H]PA), [1-¹⁴C]arachidonate ([¹⁴C]AA) and [1-¹⁴C]docosahexaenoate ([¹⁴C]DHA) — were measured using quantitative autoradiography in 11 bilateral brain visual areas of 3.5-month-old awake, hooded, Long-Evans rats, and were compared with regional cerebral metabolic rates for glucose (rCMR_glc). The rats, which had undergone unilateral orbital enucleation at 15 days of age, were studied either in the dark with eyelids of the intact eye sutured, or when stimulated in a light ? with the intact eye open. rCMR_glc did not differ between homologous contralateral and ipsilateral visual areas in the dark or during stimulation, but was elevated bilaterally by 25% or more in many visual areas during stimulation compared with dark. Contralateral compared with ipsilateralk^* was lower for each fatty acid tracer in superficial gray of the superior colliculus (in dark and during stimulation) and dorsal nucleus of lateral geniculate body (during stimulation). In the dark,k^* for [³H]PA was correlated significantly with rCMR_glc for the 22 visual areas studied, whereas during stimulationk^* for [¹⁴C]AA was correlated with rCMR_glc. These results suggest that central neuroplastic changes following chronic unilateral enucleation are accompanied by reduced incorporation of [³H]PA, [¹⁴C]AA and [¹⁴C]DHA into contralateral brain areas that normally receive crossed retinofugal fibers, and by symmetry of rCMR_glc in the dark but increased bilateral symmetrical responsiveness of rCMR_glc to visual stimulation of the intact eye.     

The novel anticonvulsant MK-801: a potent and specific ligand of the brain phencyclidine/gd-receptor

MK-801 (5-methyl-10, 11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine maleate) is a novel anticonvulsant agent reported to antagonize certain N-methyl-spd-aspartate (NMDA)-mediated effects non-competitively. The question arises of the mechanism underlying the anti-NMDA and anticonvulsant effects of MK-801. In the present study MK-801 is shown to be an extremely potent inhibitor of the binding of N-[³H](1-[2-thienyl]cyclohexy)piperidine) ([s3H]TCP to brain phencyclidine (PCP)/δ-receptors. It is IC₅₎ value of 3.8 ± 0.8 nM in this assay ranks it as the most potent known ligand of brain PCP/δ-receptors. Addition of MK-801 altered the apparent K_d but not the apparent B_max values for [³H]TCP binding, indicating a competitive interaction. The specificity of action of MK-801 is supported by the finding that MK-801 strongly inhibited the binding of (+)-N-[³H]allylnormetazocine ((+)-[³H]SKF 10.047) to the PCP/δ-receptor but its effect on (+)-[³H]SKF 10.047 binding to the non-PCP, haloperidol-sensitive δ-binding site was weaker by several orders of magnitude. Furthermore, MK-801 exerts PCP-like antagonistic effects upon NMDA-induced [³H]norepinephrine release. These findings support the concept that the anticonvulsant and anti-NMDA effects of MK-801 result from its being the most potent known ligand of PCP/δ-receptors.     

Altered 13C glucose metabolism in the cortico–striato–thalamo–cortical loop in the MK-801 rat model of schizophrenia

Using a modified MK-801 (dizocilpine) N-methyl--aspartic acid (NMDA) receptor hypofunction model for schizophrenia, we analyzed glycolysis, as well as glutamatergic, GABAergic, and monoaminergic neurotransmitter synthesis and degradation. Rats received an injection of MK-801 daily for 6 days and on day 6, they also received an injection of [1-¹³C]glucose. Extracts of frontal cortex (FCX), parietal and temporal cortex (PTCX), thalamus, striatum, nucleus accumbens (NAc), and hippocampus were analyzed using ¹³C nuclear magnetic resonance spectroscopy, high-performance liquid chromatography, and gas chromatography–mass spectrometry. A pronounced reduction in glycolysis was found only in PTCX, in which ¹³C labeling of glucose, lactate, and alanine was decreased. ¹³C enrichment in lactate, however, was reduced in all areas investigated. The largest reductions in glutamate labeling were detected in FCX and PTCX, whereas in hippocampus, striatum, and Nac, ¹³C labeling of glutamate was only slightly but significantly reduced. The thalamus was the only region with unaffected glutamate labeling. γ-Aminobutyric acid (GABA) labeling was reduced in all areas, but most significantly in FCX. Glutamine and aspartate labeling was unchanged. Mitochondrial metabolites were also affected. Fumarate labeling was reduced in FCX and thalamus, whereas malate labeling was reduced in FCX, PTCX, striatum, and NAc. Dopamine turnover was decreased in FCX and thalamus, whereas that of serotonin was unchanged in all regions. In conclusion, neurotransmitter metabolism in the cortico–striato–thalamo–cortical loop is severely impaired in the MK-801 (dizocilpine) NMDA receptor hypofunction animal model for schizophrenia.     

Differential effect of NMDA and AMPA receptor blockade on protein synthesis in the rat infarct borderzone

We investigated whether the known neuroprotective effects of two selective glutamate receptor antagonists, the NMDA antagonist MK-801 and the AMPA antagonist NBQX, are reflected in the regional cerebral protein synthesis rates (CPSR) in rats with middle cerebral artery occlusion (MCAO). Rats treated with either saline, MK-801 (5 mg/kg i.p.) or NBQX (30 mg/kg i.p. × 3) were subjected to permanent MCAO. Regional CPSR and volumes of gray matter structures displaying normal CPSR were measured in coronal cryosections of the brain by quantitative autoradiography following an i.v. bolus injection of ³⁵S-labelled l -methionine 2 h after occlusion. MCAO completely inhibited protein synthesis in the lateral part of striatum and part of the adjacent frontoparietal cortex corresponding to the ischemic focus. Surrounding this, a metabolic penumbra with approximately 50% reductions in CPSR was present. Treatment with MK-801 significantly increased the volume of tissue with normal CPSR in the ischemic hemisphere compared to controls, whereas this was not seen with NBQX treatment. The results suggest that MK-801 and NBQX have different effects on periinfarct protein synthesis after MCAO. Since both compounds reduce infarct size, it is questionable that acute inhibition of protein synthesis in focal ischemia is of significant importance to the final outcome of a stroke lesion.     

(3H]MK-801 binding sites in postmortem brain regions of schizophrenic patients

Summary [³H]MK-801 binding was used as a marker for the NMDA receptor-ion channel complex in postmortem brain samples from the frontal cortex, hippocampus, putamen, entorhinal region, and amygdala of schizophrenic patients and controls. In schizophrenia [³H]MK-801 binding levels were increased in all brain regions investigated reaching significance in the putamen.     

Washable endogenous substances and regional heterogeneity in agonist enhanced [H]MK-801 binding in rat brain

NMDA receptor/ion channel function is modulated through a number of distinct sites that regulate channel opening. Published studies report widely varying results in modulatory site agonist effects due to assay conditions and technique. Also, NMDA receptor regulation at these sites by endogenous substances remains poorly characterized. The objectives of the present study in Sprague-Dawley rat forebrain sections were: (i) determine the contribution of various prewash variables on agonist stimulation of the NMDA receptor, (ii) compare regional differences in functional glycine, spermidine and NMDA binding sites under optimized prewash conditions, and (iii) define the influence of endogenous substances at each modulatory site by analyzing changes in binding at different prewash durations. We demonstrate that prewash conditions have a critical influence on [³H]MK-801 binding in rat tissue sections and that this effect was differentially expressed across brain regions. An extended prewash duration caused a regionally specificdecrease in unenhanced [³H]MK-801 binding, while a short prewash caused a regionally specific biphasic effect on enhanced [³H]MK-801 binding. After prolonged prewash, binding was restored to previous (unwashed) binding levels with exogenously added glycine, NMDA, or spermidine alone or combinations of agonists. These data suggest that washable endogenous substances contribute to the full functionality of the NMDA receptor and the regional heterogeneity in [³H]MK-801 binding is dependent on the interaction of receptor protein subtypes and the presence of one or more endogenous substances.     

[H]MK-801 binding to the NMDA receptor complex, and its modulation in human frontal cortex during development and aging

[³H]MK-801 binding was found to decline with age in well washed membranes from human frontal cortex taken from an age series from 24 weeks gestation to 100 years old. The decline was significant under basal conditions (no added modulators) (P < 0.01), and highly significant under stimulation with glutamate, glycine and spermidine alone and in combination (P < 0.001). Scatchard analysis in the presence of glutamate and glycine showed this decline was due to a loss in the number [³H]MK-801 binding sites rather than a change in the affinity of the binding site. There was a highly significant age related reduction in the attenuation of [³H]MK-801 binding by zinc (P < 0.001). In foetal and neonatal cases up to 7 weeks of age spermidine behaved in an antagonistic manner, inhibiting rather than stimulating [³H]MK-801 binding, when alone or in the presence of glutamate and glycine. The changes in influence of glutamate, glycine, spermidine and zinc on [³H]MK-801 binding during development and aging were not due to other pre- or postmortem factors. The reverse effect of spermidine in the foetal and neonatal cases has therapeutic implications in the treatment of neonates with antiischaemic agents whose action involves the polyamine site.     

The time course of glucose metabolism in rat cerebral ischemia with middle cerebral artery occlusion-reperfusion model and the effect of MK-801

Abstract

Following cerebral ischemiai, the extracellular concentration of excitatory amino acids increases, and the excitatory cell death may play an important role contributing to ischemic neuronal damage. Although sequential metabolic changes in permanent local cerebral ischemia have been reported\ the effect of reperfusion in local cerebral ischemia on glucose metabolism is less clear. In order to investigate the time course change of glucose metabolism in a middle cerebral artery occlusion-reperfusion model and the effect of dizocilpin (MK-801) on glucose metabolism, the 4C-Deoxyglucose method was used. Hypermetabolism occurred at 30 min after the middle cerebral artery (MCA) occlusioni, and reached a peak at 60 min after ischemia in both ischemic core and penumbra. The shift from hyper- to hypometabolism was observed after the ischemia. The reperfusion facilitated the decrease of cerebral glucose metabolism in the ischemic region following 2 h of MCA occlusion. The pretreatment of MK-801 (0.4 mg kg~ 7J inhibited both increased glucose metabolism during ischemia and decreased glucose metabolism during reperfusion. These findings support the hypothesis that excitation-induced hypermetabolism plays a major role in the ischemic insult following focal cerebral vascular occlusion. [Neurol Res 1996; 18: 505-508]     

Differential inhibition by ferrous ions of [H]MK-801 binding to native N-methyl- -aspartate channel in neonatal and adult rat brains

In vitro addition or pretreatment with ≥1 μM ferrous chloride markedly inhibited in a concentration-dependent manner [³H]dizocilpine (MK-801) binding to an open ion channel associated with the N-methyl- -aspartate (NMDA) receptor in rat brain synaptic membranes. The addition of NMDA agonists invariably attenuated the inhibition of [³H]MK-801 binding in hippocampal synaptic membranes previously treated with ferrous chloride, without significantly affecting that in cerebellar synaptic membranes. In the absence of spermidine, ferrous chloride was more potent in inhibiting binding in the cerebral cortex and hippocampus in adult rats than in those in rats at 3 days after birth, while in the striatum [³H]MK-801 binding was 10 times more sensitive to inhibition by added ferrous chloride in neonatal rats than in adult rats. Addition of spermidine significantly attenuated the potency of ferrous chloride to inhibit binding in the cerebral cortex of adult rats, with facilitation of the inhibition in newborn rats. Moreover, spermidine significantly reduced the inhibitory potency of ferrous chloride in neonatal rat striatum, without markedly affecting that in adult rat striatum. These results suggest that ferrous ions may interfere with opening processes of the native NMDA channel through molecular mechanisms peculiar to neuronal development in a manner associated with the polyamine recognition domain.     

Sequelae of parenteral domoic acid administration in rats: comparison of effects on different metabolic markers in brain

Parenterally administered domoic acid, a structural analog of the excitatory amino acids glutamic acid and kainic acid, has specific effects on brain histology in rats, as measured usung different anatomic markers. Domoic acid-induced convulsions affects limbic structures such as hippocampus and entorhinal cortex, and different anatomic markers can detect these neurotoxic effects to varying degrees. Here we report effects of domoic acid administration on quantitative indicators of brain metabolism and gliosis. Domoic acid, 2.25 mg/kg i.p., caused stereotyped behavior and convulsions in approximately 60% of rats which received it. Six to eight days after domoic acid or vehicle administration, the animals were processed to measure regional brain incorporation of the long-chain fatty acids [1-¹⁴C]arachidonic acid ([¹⁴C]AA) and [9,10-³H]palmitic acid ([³H]PA), or regional cerebral glucose utilization (rCMR_glc) using 2-[1-¹⁴C]deoxy-

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-glucose, by quantitative autoradiography. Others rats were processed to measure brain glial fibrillary acidic protein (GFAP) by enzyme-linked immunosorbent assay. Domoic acid increased GFAP in the anterior portion of cerebral cortex, the caudate putamen and thalamus compared with vehicle. However, in rats that convulsed after domoic acid GFAP was significantly increased throughout the cerebral cortex, as well as in the hippocampus, septum, caudate putamen, and thalamus. Domoic acid, in the absence of convulsions, decreased relative [¹⁴C]AA incorporation in the claustrum and pyramidal cell layer of the hippocampus compared with vehicle-injected controls. In the presence of convulsions, relative [¹⁴C]AA incorporation was decreased in hippocampus regions CA1 and CA2. Uptake of [³H]PA into brain was unaffected. Relative rCMR_glc decreased in entorhinal cortex following domoic acid administration with or without convulsions. These results suggest that acute domoic acid exposure affects discrete brain circuits by inducing convulsions, and that domoic acid-induced convulsions cause chronic effects on brain function that are reflected in altered fatty acid metabolism and gliosis. © 1977 Elsevier Science B.V. All rights reserved.     

Crucial role of kainate receptors in mediating striatal kainate injection-induced decrease in acetylcholine M1 receptor binding in rat forebrain

We investigated the roles of kainate-, α-amino-3-hydroxy-5-methylisoxazol-4-propionate (AMPA)- and N-methyl- -aspartate (NMDA)-receptors in mediating striatal kainate injection-induced decrease in the binding of acetylcholine M₁ receptors in rat forebrain. After unilateral intrastriatal injection of kainate (4 nmol), the bindings of [³H]kainate (10 nM), [³H]MK-801 (4 nM) and [³H]pirenzepine (4 nM) to the rat ipsilateral forebrain membranes declined, reaching the lowest on day 2 to 4 and recovering on day 8. Saturation binding studies, performed on day 2 post-injection, showed that kainate (1, 2, 4 nmol) dose-dependently decreased B_max and K_d of the three ligands. (+)-5-Methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801), a selective NMDA receptor channel blocker, antagonised (from a dose of 4 nmol) kainate-induced decreases in the bindings of [³H]kainate (up to 20%), [³H]MK-801 (up to 90%) and [³H]pirenzepine (up to 70%). In contrast, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a selective non-NMDA receptor antagonist, almost completely abolished (from a dose of 12 nmol) kainate-induced decreases in the bindings of all the three ligands (up to 95–98%). Cyclothiazide, a selective potentiator that enhances AMPA receptor-mediated responses, significantly enhanced (from a dose of 4 nmol) kainate-induced decrease in the binding of [³H]kainate but not that of [³H]pirenzepine or [³H]MK-801. In summary, these results indicate that striatal kainate injection-induced decrease in the binding of acetylcholine M₁ receptors in rat forebrain is dependent on activation of kainate receptors and, to a certain extent, a consequent involvement of NMDA receptors. These and previous studies provide some evidence showing that kainate receptors might play a crucial role in regulating excitatory amino acids (EAA)-modulated cholinergic neurotransmission in the central nervous system (CNS).     

Supporting evidence for negative modulation by protons of an ion channel associated with theN-methyl-D-aspartate receptor complex in rat brain using ligand binding techniques

The addition ofL-glutamic acid (Glu) alone, both Glu and glycine (Gly) or Glu/Gly/spermidine (SPD) was effective in potentiating[³H]5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801) binding before equilibrium to an ion channel associated with theN-methyl-D-aspartate (NMDA) receptor complex in brain synaptic membranes extensively washed and treated with Triton X-100. The binding dependent on Glu almost linearly increased in proportion to decreasing proton concentrations at a pH range of 6.0 to 9.0 in external incubation medium, while a Gly-dependent portion of the binding increased with decreasing proton concentrations up to a pH of 7.5 with a plateau thereafter. In contrast, the SPD-dependent binding increased in proportion to decreasing proton concentrations up to a pH of 7.0 with a gradual decline thereafter. Similar profiles were also obtained with [³H]MK-801 binding at equilibrium, with an exception that significant binding of [³H]MK-801 was detected in the absence of any added agonists. The potency of SPD to potentiate [³H]MK-801 binding before equilibrium increased in proportion to decreasing proton concentrations, with those of both Glu and Gly being unchanged. In contrast, the ability of (+)MK-801 to displace [³H]MK-801 binding at equilibrium was not significantly affected by a decrement of external proton concentrations from pH 7.5 to pH 8.5 in the presence of Glu/Gly and Glu/Gly/SPD added. However, similar changes in external proton concentrations did not similarly affect binding of several radioligands for the NMDA and Gly domains on the receptor complex. Decreasing proton concentrations were effective in exponentially potentiating binding of [³H]SPD at a pH range of 6.0 to 9.0 without virtually altering [³H]D, L-α-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid binding. In addition, [³H]kainic acid binding markedly decreased with decreasing proton concentrations only in the presence of Ca²⁺ ions. These results suggest that protons negatively modulate neuronal responses mediated by the NMDA receptor ionophore complex through interference with opening mechanisms of the channel domain without disturbing association processes of the endogenous agonists with the respective recognition domains in rat brain. Moreover, possible modulation by protons of responses mediated by the kainate receptor in the presence of Ca²⁺ ions at concentrations that occur in vivo is also suggested.     

AMPA receptor antagonism attenuates MK-801-induced hypermetabolism in the posterior cingulate cortex

The effect of pretreatment with an AMPA receptor antagonist, NBQX, on MK-801-induced alterations in glucose use was examined using [¹⁴C]-2-deoxyglucose autoradiography. NBQX (7 mg/kg) had minimal effect on glucose utilisation in all anatomical regions examined. The intravenous administration of MK-801 (0.2 mg/kg) induced increases in glucose use in the limbic system and cingulate cortex. MK-801 reduced glucose utilisation in the sensory motor and auditory cortices. Pretreatment with NBQX attenuated the MK-801-induced hypermetabolism in the posterior cingulate cortex. The decreases in glucose utilisation induced by MK-801 were not exacerbated by the pretreatment with NBQX. The interaction between NBQX and MK-801 suggests a possible method of attenuating some of the adverse effects of the non-competitive NMDA receptor antagonists in the posterior cingulate cortex.     

NMDA-induced increase in [Ca]i andCa uptake in acutely dissociated brain cells derived from adult rats

A preparation of acutely dissociated brain cells derived from adult (3-month-old) rat has been developed under conditions preserving the metabolic integrity of the cells and the function of N-methyl-d-aspartate (NMDA) receptors. The effects of glutamate and NMDA on [Ca²⁺]_i measured with fluo3 and⁴⁵Ca²⁺ uptake have been studied on preparations derived from hippocampus and cerebral cortex. Glutamate (100 μM) and N-methyl-dl-aspartate (200 μM) increased [Ca²⁺]_i by 26-12 nM and 23-9 nM after 90 s in cerebral cortex and hippocampus, and stimulated⁴⁵Ca²⁺ uptake about 16–10% in the same regions. The increases in [Ca²⁺]_i and⁴⁵Ca²⁺ uptake were inhibited by 40% in the presence of 1 mM MgCl₂ and by 90–50% in the presence of MK-801. The results indicate (a) that a large fraction of the [Ca²⁺]_i response to glutamate in freshly dissociated brain cells from the adult rat involves NMDA receptors, (b) when compared with results in newborn rats, there is a substantial blunting of the [Ca²⁺]_i increase in adult age.     

Chronic treatment with the uncompetitive NMDA receptor antagonist memantine influences the polyamine and glycine binding sites of the NMDA receptor complex in aged rats

Summary Receptor binding studies on rat cortical membranes were used to characterize the NMDA receptor in aged rats (22 months) treated for 20 months with a memantine containing diet delivering 30 mg/kg/day in comparison to aged and young/adult rats treated with control-diet. Spatial memory impairing effects of (+)-MK-801 (0.16 mg/kg) in the radial maze was not altered within the course of memantine-treatment (up to 16 months). However, chronic memantine-treatment significantly increased the number of [³H]MK-801 binding sites and the affinity of [³H]glycine. A non-significant trend to such changes was also seen in aged-control rats. Glycine-dependent [³H]MK-801 binding (functional binding under non-equilibrium conditions at a fixed L-glutamate concentration) revealed that a decreased ability of glycine to stimulate channel opening in aged rats was partially attenuated by the long-term memantine treatment. Furthermore, an increased ability of spermidine to enhance [³H]MK-801 binding in aged-control rats was even more pronounced in the aged memantine-treated group. Together these findings may indicate that changes in functional receptor-channel properties during the process of aging occur prior to a detectable loss of binding sites and that memantine enhances an endogenous compensatory mechanism triggered by glutamatergic hypofunction which is suggested to take place in aging.     

Age-Related Changes in the N-Methyl- -aspartate Receptor Binding Sites within the Human Basal Ganglia

The present study examined the regional differences in dopamine transporter binding sites and NMDA receptor complex binding based on autoradiographic images obtained in postmortem sections of human normal brain tissues. In middle-aged control tissues, high and comparable levels of [³H]CFT binding were observed in the caudate nucleus, putamen, and accumbens nucleus without significant alteration along the rostrocaudal axis and ventral and dorsal parts of these nuclei. In aging normal brain tissues, dopamine binding sites for [³H]CFT were significantly reduced in the caudate nucleus, putamen, and accumbens nucleus. -[³H]Glutamate, [³H]MK-801, and [³H]glycine binding to the NMDA receptor complex was lower in aging brain tissues than in middle-aged controls. Significant correlation did occur between age and [³H]CFT binding and between age and -[³H]glutamate, [³H]MK-801, and [³H]glycine binding sites. These results demonstrate that the basal ganglia have age-associated reductions in dopamine transporter uptake and NMDA receptors. These data support hypoactive activity of the NMDA receptor complex system with advancing age. The dopamine transporter uptake and NMDA receptors appear to be vulnerable to the aging process in the basal ganglia.     

Influence of 100% and 40% oxygen on penumbral blood flow,oxygen level,and T2*-weighted MRI in a rat stroke model

Accurate imaging of the ischemic penumbra is a prerequisite for acute clinical stroke research. T₂^* magnetic resonance imaging (MRI) combined with an oxygen challenge (OC) is being developed to detect penumbra based on changes in blood deoxyhemoglobin. However, inducing OC with 100% O₂ induces sinus artefacts on human scans and influences cerebral blood flow (CBF), which can affect T₂^* signal. Therefore, we investigated replacing 100% O₂ OC with 40% O₂ OC (5 minutes 40% O₂ versus 100% O₂) and determined the effects on blood pressure (BP), CBF, tissue p₂, and T₂^* signal change in presumed penumbra in a rat stroke model. Probes implanted into penumbra and contralateral cortex simultaneously recorded p₂ and CBF during 40% O₂ (n=6) or 100% O₂ (n=8) OC. In a separate MRI study, T₂^* signal change to 40% O₂ (n=6) and 100% O₂ (n=5) OC was compared. Oxygen challenge (40% and 100% O₂) increased BP by 8.2% and 18.1%, penumbra CBF by 5% and 15%, and penumbra p₂ levels by 80% and 144%, respectively. T₂^* signal significantly increased by 4.56%±1.61% and 8.65%±3.66% in penumbra compared with 2.98%±1.56% and 2.79%±0.66% in contralateral cortex and 1.09%±0.82% and −0.32%±0.67% in ischemic core, respectively. For diagnostic imaging, 40% O₂ OC could provide sufficient T₂^* signal change to detect penumbra with limited influence in BP and CBF.     

Laminar distribution of MK-801, kainate,AMPA, and muscimol binding sites in cat visual cortex: A developmental study

We used quantitative autoradiography to determine whether the development of glutamate receptors correlates with the sensitive period for monocular deprivation in the visual cortex. To study glutamate receptors, we incubated sections of cat visual cortex with tritiated (+)-5-methyl-10, 11-dihydro-5H-dibenzo[a,d]-cyclohepten-5,10imine-maleate (MK-801), tritiated kainate, and tritiated amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA). [³H]MK-801 is a noncompetitive ligand for the N-methyl-D-aspartate (NMDA) receptor. [³H]kainate and [³H]AMPA are competitive ligands for non-NMDA receptors. We used [³H]muscimol, which binds to GABA_A receptors, so that we would have one control ligand that binds to a nonglutamate receptor. When all layers were combined, the results confirmed our previous studies with homogenate binding. [³H]MK-801 and [³H]kainate binding were significantly greater at 42 days than at earlier or later times. [³H]AMPA and [³H]muscimol binding did not show such a peak. This suggests that MK-801 and kainate binding sites are more likely to be involved in plasticity than are AMPA and muscimol binding sites. In layers 2/3, MK-801 had the greatest age-dependent changes; in layers 5 and 6, kainate binding changed most with age. This suggests that the mechanisms of plasticity may vary with cortical layer. © 1996 Wiley-Liss, Inc.